Interest has heightened in use of teleosts for bioassay testing, detection of carcinogens in the environment, and as potential comparative oncology models for human cancer. However, basic questions remain on pathogenesis and biologic properties of fish tumors. The liver is sensitive to carcinogens in fish and higher vertebrates. To further development of fish as useful animal models, we will analyze aspects of hepatic carcinogenesis in two promising species, Salmo gairdneri and Oryzias latipes. Questions about: how proliferative lesions of fish liver conform to data on neoplasms in mammalian liver; morphologic characteristics of liver cells and intracellular matrix in fish neoplasms and sensitivity of intrahepatic biliary epithelial cells to carcinogens will be addressed. Coupled in vivo and in vitro studies will focus on populations of fish liver cells. Sensitive immunohistochemical probes will be used to determine effect of specific carcinogens on mitotic index, induction of unscheduled DNA synthesis (UDS) and alterations of cell and matrix glycoproteins and glycosaminoglycans. Course and fate of neoplastic liver lesions will be studied using enzyme histochemistry of altered cells and long-term follow-up of tumor laden fish. The ability of carcinogens to form specific DNA adducts will be determined by ultrasensitive mass spectrometer studies. We will seek to correlate formation to specific DNA adducts with types of liver lesions. Three specific aims are proposed. 1. Characterize morphologic events in the progression of lesions from normal liver to overt tumor in Japanese medaka as a function of age at initiation and determine long-term potential of liver cell tumors for growth/metastasis. 2. Isolate and maintain, in primary culture, liver cells of trout and develop procedures to separate nonhepatocytic cell populations. From the latter, establish long-term culture of trout biliary epithelial cells. 3. Determine capacity of hepatocytes and other cell types of trout liver to activate genotoxic carcinogens after in vitro exposure and determine extent and specific cell types in which carcinogen-induced DNA repair occurs. Determine, qualitatively and quantitatively, DNA adducts in trout liver and cells exposed to various carcinogens and follow effect of DNA repair on amount of adduct. Using carcinogen bioassay, determine compound specific effects of DNA adduct formation on repair and on carcinogenic potential.